1. Field of the Invention
This invention relates to induction watthour meters including an electromagnet assembly and more particularly to such meters having an integral magnetic flux lagging and light load adjustment assembly for calibrating and compensating line voltage responsive fluxes generated in the electromagnet assemblies thereof.
2. Description of the Prior Art
Induction watthour meters are almost universally used for billing and load monitoring of AC electric energy transmitted by an electric utility company or other electric energy supplier to residential and commercial electricity users. Voltage and current magnetic sections of the meter electromagnet assembly produce line voltage and line current responsive magnetic fluxes into an electroconductive disc so it is rotated in response to the consumption of AC electric energy. In manufacture and design of watthour meter electromagnet assemblies, it is known to provide adjustments on the voltage magnetic section so that the voltage and current fluxes rotate the disc at a calibrated rate or speed having a predetermined ratio to the measured electric energy usage in kilowatt hours. The ratio of the disc speed to the measured electric energy is often referred to as the watthour constant of the meter.
Correction and adjustment of the power factor or voltage flux phase lag and light load characteristics are two common calibrating adjustments of induction watthour meters. The calibrations are used to provide operation in accordance with the well-known basic theory of operation of induction watthour meters which includes the principle that the magnetic flux from the voltage section, being responsive to the line voltage, must lag the magnetic flux from the current section, being responsive to the line current, by ninety electrical degrees when the line voltage and current are in phase at unity power factor. In modern watthour meters, the voltage and current fluxes are directed in the quadrature phase relationship in opposing directions into an air gap space and into opposite sides of the meter disc in the gap. The fluxes produce eddy currents in localized areas of the disc. In accordance with the aforementioned basic theory, interaction of the eddy currents with the voltage and current magnetic fluxes develops torque on the meter disc in proportion to the measured electrical energy. A coil having a large number of small conductor winding turns is typically mounted on the center leg of an E-shaped magnetic core of the voltage section. This voltage coil has substantial inductance so that the voltage air gap flux produced by the coil will substantially lag the line voltage but not by ninety degrees without further adjustment. To provide the additional flux lagging adjustment, it is known to provide a loop of conductive material around the voltage flux so that circulating current is induced therein to establish a further voltage flux component that is vectorially added to the voltage coil main flux component to produce a corrected working voltage flux in the disc air gap space. The resultant air gap voltage flux has substantially the aforementioned ninety degrees or quadrature lagging relationship with the line voltage and the current flux at unity power factor. It is further important that the calibrated values provided by the adjustments be maintained during mechanical shocks and vibrations occurring during shipping and handling of the meters.
One example of a voltage conductive lag loop is disclosed in U.S. Pat. No. 2,879,476. A second electroconductive loop forms a light load adjustment element. Both the lag loop and the light load loop members are movably mounted on a separate bracket attached to the side of the magnetic core of the meter electromagnet. In U.S. Pat. No. 2,057,443, a rectangular plate with a center hole surrounds the voltage magnetic pole to provide the ninety degree voltage flux lag or quadrature relationship with the current flux. One or two laminations of the core are bent to prevent shifting of the lagging quadrature plate. A separately-supported vernier lag adjuster plate is moved at right angles to the direction of disc torque by a worm gear adjusting element mounted on one side of the quadrature plate. A torque adjuster plate is also provided for multi-element meter electromagnets. In U.S. Pat. No. 2,352,965, a lag coil is made of a conductive material and is provided with an adjustable lag plate part for varying the resistance. A magnetic strap is clamped to the adjustable lag plate so that a small percentage of the voltage main pole flux is diverted and lagged and may be shifted for light load adjustment so that the disc torque can be shifted in either direction.
Light load adjustment differs from the phase lag adjustment so that at low values of line current an unsymmetrical component of voltage flux will add torque to the meter disc. A part of the light load adjustment compensates for the slight frictional drag on the meter disc shaft and another part compensates for the non-linear and lower permeability characteristics of the laminated magnetic core materials at low magnetic induction causing the line current related flux to be disproportionately low. Compensation and calibration of the light load adjustment in some electromagnet assemblies, and in the present invention, is related to the regulation of the disc torque producing magnetic drive effects of a secondary voltage flux path established between the meter disc and a pair of auxiliary voltage pole faces. The secondary voltage flux path is divided and extends between the disc and the pair of auxiliary voltage poles formed at the free ends of the outside legs of an E-shaped voltage core on opposite sides of the main voltage pole face. The secondary flux path produces secondary torques on the disc in opposite directions. A light load adjuster is described in U.S. Pat. No. 2,947,942 which includes two magnetic members movable over the auxiliary pole faces. The magnetic members produce dissymmetry in the disc torque producing effects of the secondary flux path in a predetermined aiding relationship to the main driving torque on the disc. The magnetic members are movably mounted on a brass bracket fastened to the meter electromagnet assembly and the bracket also carries a threaded adjusting member to move the magnetic members. In U.S. Pat. No. 3,493,862, assigned to the assignee of this invention, a light load adjuster is described including soft magnetic members carried by a nonmagnetic bracket. The magnetic members are pivotally mounted on the bracket so that the ends of the members extend over the faces of the voltage flux arms to vary light load calibrations.
The aforementioned prior art voltage section adjustment arrangements do not provide voltage flux lagging loop adjustment member formed integrally with a bracket attached to the voltage magnetic core to add strength and rigid spacing of the core outer legs while providing a mounting platform for a light load adjustment member having two magnetic members movable across the voltage auxiliary pole faces to provide a predetermined light load disc torque adjustment nor provide an integral assembly having a lag loop tightly secured in place so as to prevent changes in calibration when subjected to shock.